Chapter 2-

NOTICEExtra slides are added to the original slide.

1

Chapter 2-

Nucleus: Z = # protons

2

orbital electrons: n = principal quantum number

n=3 2 1

= 1 for hydrogen to 94 for plutoniumN = # neutrons

Atomic mass A ≈ Z + N

Adapted from Fig. 2.1,

Callister 6e.

BOHR ATOM

Chapter 2-

• have discrete energy states

• tend to occupy lowest available energy state.

3

Electrons...

Adapted from Fig. 2.5,

Callister 6e.

ELECTRON ENERGY STATES

Chapter 2- 4

• have complete s and p subshells

• tend to be unreactive.

Stable electron configurations...

Adapted from Table 2.2,

Callister 6e.

STABLE ELECTRON CONFIGURATIONS

Chapter 2- 5

• Why? Valence (outer) shell usually not filled completely.

• Most elements: Electron configuration not stable.

Electron configuration 1s1

1s2 (stable) 1s22s1 1s22s2 1s22s22p1 1s22s22p2 ...

1s22s22p6 (stable) 1s22s22p63s1 1s22s22p63s2 1s22s22p63s23p1 ...

1s22s22p63s23p6 (stable) ...

1s22s22p63s23p63d104s246 (stable)

Adapted from Table 2.2,

Callister 6e.

SURVEY OF ELEMENTS

Chapter 2- 6

• Columns: Similar Valence Structure

Electropositive elements:

Readily give up electrons

to become + ions.

Electronegative elements:

Readily acquire electrons

to become - ions.

Adapted

from Fig. 2.6,

Callister 6e.

THE PERIODIC TABLE

Chapter 2- 7

• Ranges from 0.7 to 4.0,

Smaller electronegativity Larger electronegativity

• Large values: tendency to acquire electrons.

Adapted from Fig. 2.7, Callister 6e. (Fig. 2.7 is adapted from Linus Pauling, The Nature of the Chemical Bond, 3rd edition, Copyright 1939 and 1940, 3rd edition. Copyright 1960 by Cornell

University.

ELECTRONEGATIVITY

Chapter 2- 8

• Occurs between + and - ions.

• Requires electron transfer.

• Large difference in electronegativity required.

• Example: NaCl

IONIC BONDING

Chapter 2-

Characteristics of Ionic Bonding

• 1. medium high melting point (600 - 2000° C)

• 2. medium high boiling points

• 3. hard and brittle

• 4. nonconductor of electricity

• 5. poor conductor of heat

Chapter 2- 9

• Predominant bonding in Ceramics

Give up electrons Acquire electrons

He -

Ne -

Ar -

Kr -

Xe -

Rn -

F 4.0

Cl 3.0

Br 2.8

I 2.5

At 2.2

Li 1.0

Na 0.9

K 0.8

Rb 0.8

Cs 0.7

Fr 0.7

H 2.1

Be 1.5

Mg 1.2

Ca 1.0

Sr 1.0

Ba 0.9

Ra 0.9

Ti 1.5

Cr 1.6

Fe 1.8

Ni 1.8

Zn 1.8

As 2.0

CsCl

MgO

CaF2

NaCl

O 3.5

Adapted from Fig. 2.7, Callister 6e. (Fig. 2.7 is adapted from Linus Pauling, The Nature of the Chemical Bond, 3rd edition, Copyright 1939 and 1940, 3rd edition. Copyright 1960 by Cornell

University.

EXAMPLES: IONIC BONDING

Chapter 2- 10

• Requires shared electrons

• Example: CH4

C: has 4 valence e,

needs 4 more

H: has 1 valence e,

needs 1 more

Electronegativities

are comparable.

Adapted from Fig. 2.10, Callister 6e.

COVALENT BONDING

Chapter 2-

Characteristics of Covalent Bonding

• 1. very low melting point (-370 to 300° C)

• 2. very low boiling point

• 3. soft

• 4. nonconductor of electricity

• 5. poor conductor of heat

Chapter 2- 11

• Molecules with nonmetals• Molecules with metals and nonmetals• Elemental solids (RHS of Periodic Table)• Compound solids (about column IVA)

He -

Ne -

Ar -

Kr -

Xe -

Rn -

F 4.0

Cl 3.0

Br 2.8

I 2.5

At 2.2

Li 1.0

Na 0.9

K 0.8

Rb 0.8

Cs 0.7

Fr 0.7

H 2.1

Be 1.5

Mg 1.2

Ca 1.0

Sr 1.0

Ba 0.9

Ra 0.9

Ti 1.5

Cr 1.6

Fe 1.8

Ni 1.8

Zn 1.8

As 2.0

SiC

C(diamond)

H2O

C 2.5

H2

Cl2

F2

Si 1.8

Ga 1.6

GaAs

Ge 1.8

O 2.0

co

lum

n I

VA

Sn 1.8

Pb 1.8

Adapted from Fig. 2.7, Callister 6e. (Fig. 2.7 is

adapted from Linus Pauling, The Nature of the Chemical Bond, 3rd edition, Copyright

1939 and 1940, 3rd edition. Copyright 1960 by Cornell University.

EXAMPLES: COVALENT BONDING

Chapter 2- 12

• Arises from a sea of donated valence electrons(1, 2, or 3 from each atom).

• Primary bond for metals and their alloys

Adapted from Fig. 2.11, Callister 6e.

METALLIC BONDING

Chapter 2-

Characteristics of Metalic Bonding

• 1. very low to very high melting point

• 2. very low to very high boiling point

• 3. very soft to very hard

• 4. ductile and malleable

• 5. good conductor of heat and electricity

Chapter 2- 13

Arises from interaction between dipoles

• Permanent dipoles-molecule induced

• Fluctuating dipoles

-general case:

-ex: liquid HCl

-ex: polymer

Adapted from Fig. 2.13, Callister 6e.

Adapted from Fig. 2.14,

Callister 6e.

Adapted from Fig. 2.14,

Callister 6e.

SECONDARY BONDING

Chapter 2- 14

Type

Ionic

Covalent

Metallic

Secondary

Bond Energy

Large!

Variablelarge-Diamondsmall-Bismuth

Variablelarge-Tungstensmall-Mercury

smallest

Comments

Nondirectional (ceramics)

Directional

semiconductors, ceramicspolymer chains)

Nondirectional (metals)

Directionalinter-chain (polymer)

inter-molecular

SUMMARY: BONDING

Chapter 2- 15

• Bond length, r

• Bond energy, Eo

F F

r

• Melting Temperature, Tm

Tm is larger if Eo is larger.

PROPERTIES FROM BONDING: TM

Chapter 2- 16

• Elastic modulus, E

• E ~ curvature at ro

L F

Ao = E

Lo

Elastic modulus

r

larger Elastic Modulus

smaller Elastic Modulus

Energy

ro unstretched length

E is larger if Eo is larger.

PROPERTIES FROM BONDING: E

Chapter 2- 17

• Coefficient of thermal expansion, a

• a ~ symmetry at ro

a is larger if Eo is smaller.

= a(T2-T1) L

Lo

coeff. thermal expansion

PROPERTIES FROM BONDING: a

Chapter 2- 18

Ceramics

(Ionic & covalent bonding):

Metals

(Metallic bonding):

Polymers(Covalent & Secondary):

Large bond energylarge Tm

large E

small a

Variable bond energymoderate Tm

moderate E

moderate a

Directional PropertiesSecondary bonding dominates

small T

small E

large a

SUMMARY: PRIMARY BONDS